This invention relates generally to electric spark discharge recording. More particularly the invention relates to a novel non-impact dot matrix printer of the type that prints alpha-numeric characters on an electrical conductive and erosive surface of a recording medium. The novel printer is particularly useful for, although not limited to, alpha-numeric, high speed, digital communications and computer outputs.
Non-impact printing by electric discharge (electroerosion) printing means to print characters on an electrosensitive recording medium was accomplished in the prior art primarily by means of contacting styli mounted on a printing head assembly that moved across the recording medium for printing each line of characters. Such prior-art printing apparatus comprised many moving parts, such as the printing head assembly, electrical conductors attached to the styli of the head, and drive means for the head; and these moving parts were potential sources of mechanical failure.
It has been disclosed in U.S. Pat. No. 3,711,860 for an "Arc Discharge Recording Apparatus with Pigment Carrier" to provide a printing system with an apertured, rotatable belt of dielectric material that moved across a recording surface of a non-erosive recording medium along a recording line. A pigmented carrier was positioned between the belt and a first electrical conductor, and a second electrical conductor supported the recording medium on a surface opposite to the recording surface. A selectively operable high voltage was applied between the first and second electrical conductors to induce an electrical discharge through the pigmented carrier, the aperture in the moving belt, and the recording surface. The electrical discharge transferred some of the pigment from the carrier to the non-erosive recording surface to produce a visible recording on the recording surface. This prior-art apparatus was a pigment deposition scheme for producing graphs on a medium that was not electroerosive, along two axes, and the apparatus could not be used for an alpha-numeric dot matrix printer.